1. Field of the Invention
The present invention relates to a zoom lens system and an image pickup apparatus using the same.
2. Description of the Related Art
In recent years, instead of a silver halide film camera, a digital camera has been a mainstream which photographs a subject by use of an electronic image pickup device such as a CCD image sensor or a CMOS type image sensor. Furthermore, the camera has been used in a large number of categories in a broad range from a highly functional type for business to a compact popular type. A user of the popular type of digital camera would like a small-sized camera, especially a digital camera of a thin type which is conveniently carried with a good storage property in clothing, a bag pocket or the like and which has a small size in a thickness direction.
On the other hand, a zoom ratio of a photographing lens has been generally about three, but there is a demand for a camera having a high zoom ratio and capable of photographing with a large angle of view in order to satisfy users' broad needs.
The photographing lens for such a camera needs to be miniaturized so that portability of the camera is not impaired.
A zoom lens system having a large zoom ratio and a large angle of view of 70° or more in a wide-angle end is disclosed in the following documents 1) to 7).
To thin the camera, a lens barrel of the photographing lens needs to be thinned. As means for thinning the photographing lens, a so-called collapsible lens barrel has been generalized which is projected from a camera body at a time when the camera has a photographing state and which is stored in the camera body when carried. Therefore, it is important to form a zoom lens system in consideration of the thinning of the collapsed lens barrel. Specifically, to reduce the thickness of the lens barrel when collapsed, each lens unit of the zoom lens system needs to include less lenses, and a total length of the zoom lens system needs to be shortened.
1) Japanese Patent Application Laid-Open No. 7-5,361
2) Japanese Patent Application Laid-Open No. 7-20,381
3) Japanese Patent Application Laid-Open No. 8-50,244
4) Japanese Patent Application Laid-Open No. 2001-350,092
5) Japanese Patent Application Laid-Open No. 2005-17,915
6) Japanese Patent Application Laid-Open No. 2006-78,979
7) Japanese Patent Application Laid-Open No. 2006-235,062